The overall objective of the proposed project is to study the coding of tactile stimuli in neural circuits from the face. The rat is used as the experimental animal, and the mystacial virissae, which the rat employs extensively in exploration of its mechanosensory environment, are the sensory structures stimulated by quantitatively controlled mechanical stimuli. Four specific objectives are included in the overall goal: (1) To describe stimulus-response (S-R) relationships of populations of single neurons in the trigeminal complex using a broad battery of precisely-controlled stimulus waveforms and a variety of quantitative data analysis procedures; (2) To determine whether neurons in the different subnuclei of the trigeminal complex exhibit different S-R properties; (3) To define the changes in stimulus-response relationships that occur between first and second order levels of trigeminal tactile circuits, and (4) To determine whether axons arising from cells of the different subnuclei project into different tactile circuits. Laboratory computer methods are employed for control of both mechanosensory stimuli and of data collection and analysis. These studies will help to fill large gaps in our knowledge regarding the spatial distribution and differential specialization of neurons with different tactile coding functions within several known trigeminal sensory circuits.